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LIBRARY 


UNIVERSITY  OF 
CALIFORNIA 


CA*TH 

SCIENQGt 
UBRAKY 


LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA. 


GIFT  OF" 


Class 


A  STUDY  OF 


THE  IGNEOUS  ROCKS 


YORK  HAVEN  and  STONY  BROOK,  PA. 


THEIR   ACCOMPANYING   FORMATIONS 


THESIS 

Presented  to  the   Faculty  of  the  Department  of  Philosophy  of  the 

University  of  Pennsylvania,  in  partial 
fulfillment  of  the  requirements  for  the  degree  of  Doctor  of  Philosophy 


BY 

FREDERICK  EHRENFELD,  A.  B. 


PHILADELPHIA 


PHILADELPHIA 
AVIL  PRINTING  COMPANY 


E4 


EARTH 

SCIENCE 

LIBRARY 


INTRODUCTION. 

The  American  Triassic  in  the  region  of  the  Atlantic 
border  States  is,  as  is  well  known,  pierced  by  numerous 
igneous  eruptions  throughout  its  entire  area.  One  has 
only  to  turn  to  the  literature  of  the  Triassic  area  from 
Massachusetts  to  North  Carolina  to  obtain  an  idea  of  the 
great  numbers  of  these  dikes  and  the  variations  they  show 
in  length  and  thickness.  From  thin  sheets  of  a  few  inches 
in  thickness  we  find  all  gradations  up  to  several  hundred 
feet  in  thickness  and  many  miles  in  length. 

Furthermore,  the  forces  which  produced  these  eruptions 
in  the  Trias  by  no  means  confined  themselves  to  the  rocks 
of  that  age,  for  the  surrounding  formations  down  to  the 
Archaean  are  characterized  in  many  places  by  eruptions 
which  are  no  doubt  intimately  connected  with  those  of  the 
Trias  itself. 

In  spite  of  the  great  distance  apart  of  many  of  these 
eruptions,  their  lithological  character  is  in  general  the 
same.  They  all,  or  nearly  all,  fall  into  one  or  other  of  the 
types  known  as  dolerite,  gabbro,  diabase,  or  the  alterations 
thereof. 

In  Pennsylvania  the  area  of  these  eruptions  extends  in  a 
southwest  direction  from  the  New  Jersey  line  through  to 
and  including  York  and  Adams  counties  to  the  State  of 
Maryland.  On  the  map  of  York  county,  published  by  the 
Second  Geological  Survey  of  Pennsylvania,  ten  or  more  of 
these  dikes  have  been  indicated.  These  have  been  described 
in  a  general  way  in  the  various  reports  on  York  and  Lan- 
caster counties.1  Persifor  Frazer  discusses2  the  traps  of 

1  See  Reports  C,  CC,and  CCC  .  Second  G.  S.  Pa. 

2  Second  G.  S.  Pa.  Report  C,   pp.  115-129. 

(3) 


4 

York  and  Adams  counties,  and  refers  them  all  to  dolerite. 
With  this  exception  little  if  any  work  has  been  published 
in  regard  to  them. 

The  following  investigation  was  begun  with  the  desire  of 
studying  two  of  these  dikes  in  order  to  ascertain  what 
points  of  resemblance  or  difference  they  might  show  with 
similar  regions  elsewhere.  In  addition  to  this  work  a 
study  was  made  of  the  formations  surrounding  one  of  these 
dikes. 

The  two  localities  selected  are  at  York  Haven  and  Stony 
Brook,  both  in  York  county.  At  the  former  locality  the 
surrounding  rocks  are  Triassic,  at  the  latter  they  are 
Cambrian. 

Before  proceeding  to  a  description  of  these  dikes  it  may 
not  be  amiss  to  indicate  briefly  the  geological  structure  of 
the  part  of  York  county  referred  to. 

The  accompanying  map,  which  is  reduced  from  the 
State  Survey  map  of  York  county,  will  assist  in  making  the 
geological  structure  clear. 


GEOLOGICAL  STRUCTURE  OF  THE  REGION. 

In  passing  across  the  county  in  a  southeasterly  direction, 
or  in  following  the  course  of  the  Susquehanni  River,  the 
formations  present  themselves  in  the  following  order  :* 

New  Red  Sandstone, 

Siluro-cambrian  Limestone, 

Hydro-mica  Schist, 

Quartzite,  Potsdam, 

Chlorite  Schist, 

Azoic  Slates. 

By  the  geologists  of  the  First  Pennsylvania  Geological 
Survey,  1858,  Henry  D.  Rogers,  director,  the  limestone 
above  mentioned  was  considered  as  equivalent  to  the 
Black  River,  Chazy  or  Calciferous  of  New  York  State. 
The  quaitzite  was  regarded  as  Potsdam.  When  the  second 
survey  of  Pennsylvania  was  organized,  Dr.  Persifor  Frazer 
was  put  in  charge  of  the  survey  of  York  county,  and  he 
arranged  the  formations  in  descending  order  as  given 
above. 

In  1892,  C.  D.  Walcott,  of  the  U.  S.  Geological  Survey, 
began  an  investigation  of  the  supposed  Silurian  and  Cam- 
brian rocks  of  York  county.  The  results  of  his  work  were 
published  as  a  Bulletin  of  the  U.  S.  Survey.2  Mr.  Walcott 
places  the  above  mentioned  quartzite,  limestone  and  chlorite 
schist  in  the  Lower  Cambrian,  and  in  fact  he  regards  it  as 
doubtful  "  if  there  is  in  York  county  a  sedimentary  rock — 
other  than  the  mesozoic  New  Red  S.  S. — of  later  age  than 
Cambrian."  For  details  of  his  work  reference  must  be 
made  to  Bulletin  No.  134,  previously  mentioned. 

In  regard  to  the  New  Red  it  is  not  necessary   here  to 

iSee  map  of  York  County,  published  in  Report  Ca,  Pa.  Geo.  Survey. 
2  The  Cambrian  Rocks  of  Pa.,  by  C.  D.  Walcett,  Bull.  134,  U.  S.  G.  S. 

(5) 


fire  «.  Ac  g 


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M  i* 
K,Co 


mention  in  detail  what  has  been 
done  in  this  field  of  geological 
research.  The  literature  on  the 
subject  is  voluminous  and  has  been 
admirably  summarized  by  I.  C. 
Russell.1 

In  Pennsylvania  the  most  recent 
work  is  that  of  B.  S.  Lyman,  in 
Bucks  and  Montgomery  counties. 
From  the  results  of  his  work  Mr. 
Lyman  derives  the  following  sub- 
divisions, arranged  from  the  top 
downwards  :2 

5.  Pottstown  Shales. — Ten  thou- 
sand seven  hundred  feet  of  shales, 
mostly  soft  and  red,  with  a  few 
beds  of  limestone.  Fossils  are  ob- 
scure plant  remains  and  the  Dino- 
saur Clepsaurus  Pennsylvania  of 
Lea. 

4..  Perkasie  Shales. — Two  thou- 
sand feet  of  dark  red,  gray  or  green 
shales.  The  shales  are  in  general 
hard  and  have  several  blackish  or 
coaly  layers.  Fossils  have  not 
been  satisfactorily  made  out. 

j.  Lansdale  Shales. — Four  thou- 
sand seven  hundred  feet,  more  or 
less,  of  shales  mostly  calcareous 
and  in  large  part  red  in  color. 
There  are  a  few  scattered  green 
layers  and  a  little  soft  red  sand 
rock.  The  beds  are  in  general 
soft.  Fossils  few. 

2.  Gwynedd  Shales.  —  Three 


The  Newark  System,  by  I.  C.  Rus«ell.  Bull.   85  U.  S.  G.  S.,   1893. 
Summary  Final  Rp.P  a.  Geol.  S.  1895,  Vol.  3,  \.p.  2607  et  seq. 


7 

thousand  five  hundred  feet.  These  rocks  are  hard,  fre- 
quently very  hard.  Towards  the  top  are  dark  red,  also 
green,  gray  and  even  black,  with  a  little  coal.  From  these 
beds  have  come  most  of  the  important  fossils  of  the  Trias- 
sic.  Mr.  Lyman  places  these  beds  as  equivalent  to  those 
of  the  Richmond,  Virginia,  and  North  Carolina  exposures. 
(See  p.  2611  of  the  Report  before  cited.) 

/.  Norristown  Shales. — Six  thousand  one  hundred  feet 

This  series  makes  up  the  lowest  members  of  the  New 
Red  in  Bucks  and  Montgomery  counties.  These  rocks  are 
prevailingly  red  in  color,  particularly  at  the  bottom.  Near 
the  base  also  are  some  beds  of  coarse,  pebbly,  hard,  gray 
sand  rock.  Near  the  top  are  courses  of  brown  building 
stone.  Beds  of  this  nature  are  not  suited  for  the  preserva- 
tion of  fossils,  and,  as  a  matter  of  fact,  few  have  been  found. 

"  It  is  clear,"  says  Mr.  Lyman,  "  that  the  paleontological 
age  of  this  set  of  beds  has  never  been  satisfactorily  deter- 
mined. .  .  .  there  is  a  strong  probability  that  they  are 
Paleozoic,  at  least  as  old  as  the  Permian."  (P.  2614  of  Ly- 
man's  Report.) 

Since  Mr.  Lyman's  work  in  Pennsylvania  was  published, 
Henry  B.  Kiitnmel,1  of  the  New  Jersey  Geological  Survey, 
working  on  lithotogical  evidence,  has  divided  the  Trias  of 
that  State  into  three  divisions : 

Feet. 

Stockton  series 4.700 

Lockatong  series 3, 600 

Brunswick  shales 12,000 

20,300 
In  the  absence  of  detailed  information  of  the  character 

of  these  beds  no  correlation  of  them  with  Lyman's  may  be 

safely  attempted. 

During  the  progress  of  my  own  work  in  York  county  it 

!Am.  Rep.  G  S.  of  New  Jersey,  1896,  p.  59. 


3050' 


2900' 


2140 


__  I3°' (24) 
5MP3  90'  (23) 

285'  (15-22) 


go'  (11-14) 
90'  (8-10) 

75'  (7) 
80'  (5-6) 
'SO'  (4) 


8  .  . 

was  desired  to  obtain  an  idea  of  the  character  of  the  Trias 
below  the  dike  at  York  Haven  ;  that  is,  in  its  lower  part. 
Accordingly  a  section  was  measured 
from  the  contact  of  the  Cambrian  and 
Trias  up  to  York  Haven.  This  is 
indicated  on  the  map  by  the  line 
A-B. 

From  thestratigraphical  evidence  as 
well  as  from  the  fossils  found,  it  is  be- 
lieved that  the  position  of  these  beds 
may  be  indicated  with  some  degree 
of  accuracy.  The  thickness  is  in  all 
4350  feet.  It  is  only  fair  to  say  that 
approximate  value  only  is  claimed  for 
this  section,  especially  the  lower  part. 
The  thickness  was  obtained  by  calcu- 
lation from  the  dip  and  horizontal 
distances.  In  the  lower  part  exposure 
is  poor,  in  the  upper  part  very  good. 
The  lower  portion  for  an  estimated 
thickness  of  1960  feet  is  concealed, 
and  the  character  of  the  formation  is 
judged  from  surface  indications,  such 
as  the  color  and  other  physical  aspects 
of  the  soil.  Near  the  middle  of  the 
concealed  portion  an  outcrop  of  dark 
red,  sandy  shale  was  noted.  The 
soil  was  dark  brownish  red  in  color. 
At  a  point  three  hundred  feet  below 
this  an  outcrop  of  conglomerate  was 
seen.  The  pebbles  were  of  quartz, 
varying  in  size  from  less  than  an  inch 
in  diameter  up  to  five  or  six  inches. 
The  soil  contains  many  of  these  peb- 
bles, which  increase  in  number 


So'  (2-3) 

1 80' 


9 

towards  the  bottom.     The  dip  at  each  of  these  outcrops 
gave  an  average  of  23°  N.  W. 

At  the  top  of  this  concealed  part  the  soil  is  yellow  in 
color.  Arkose  or  granitic  sandstone  was  observed  here. 

Above  the  concealed  part  the  rocks  with  a  few  exceptions 
are  well  shown  and  their  character  was  easily  made  out. 
From  the  drawn  illustration  the  positions  of  the  different 
members  nruy  be  seen. 

DETAILED  DESCRIPTION  OF  SECTION. 

The  following  description  is  intended  to  cover  the  mem- 
bers of  the  section  above  the  concealed  part  beginning 
1960  feet  above  the  bottom.  The  numbers  refer  to  those 
given  in  parentheses  in  the  illustration  of  the  section. 

(1)  One  hundred  and  eighty  feet  of  sandstone,  mostly 
fine  grained  and  light  gray  in  color.     Fine  scales  of  mica 
and  a  little  feldspar  are  scattered  through  the  rock.     There 
is   evidence,    in   places,   of  its    having   been   deposited   in 
changing  currents.     Interspersed  with  these  sandstone  beds 
are  layers  of  shale. 

(2)  Above  the  sandstone  are  twenty  feet  of  a  soft,  crumb- 
ling red  shale,   containing   numerous    rounded   calcareous 
nodules.     Fossils   are   obscure  plant   remains   and   forms 
resembling  some  species  of  algae. 

(3)  Next  come  thirty  feet  of  a  quartz  conglomerate,  mostly 
fine  grained,  but  in  some  places  rather  coarse.     Mica  and 
pyrite  are  scattered  through  the  rock.     The  conglomerate 
is  of  a  light  color,  with  a  faint  bluish  tinge. 

With  this  conglomerate  are  beds  of  fine  grained,  grayish 
or  brownish  sandstone,  with  a  good  deal  of  mica  and  a 
small  amount  of  feldspar. 

The  formations  following  for  an  estimated  thickness  of 
seven  hundred  feet  are  concealed.  The  soil  is  sandy,  and 
toward  the  botton  is  reddish  in  color.  At  the  top  it  is 
yellowish. 


10 

(4)  On  hundred  and  fifty  feet  of  a  dark  gray,  almost  black, 
sand  rock   which   is   in   places    quite   calcareous.      Small 
fragments   of    a  soft,   shaly  material  are  occasionally  seen. 
The  rock  contains  mica  and  some  feldspar,  and  somewhat 
resembles  a  granitic  sandstone  in  appearance,  though  hardly 
to  be  classed  as  such. 

(5)  This  member  comprises  about  seventy  feet  of  shale  and 
sandstone.     At  the  bottom  are  several  feet  of  a  hard,  fine 
grained  green  sandstone,  with  small  scales  of  white  mica 
The  sandstone  in  weathering,  forms  roundish  blocks  which 
in   their   natural    position    resemble   a   wall  of    masonry. 
Closely  associated  with  this  sandstone  are  beds  of  red  and 
green  shales. 

Following  come  fifty  feet  or  so  of  sandstone.  At  the 
bottom  the  beds  are  soft  and  yellow ;  they  pass,  however, 
into  rather  coarse  gray  or  green  layers,  containing  a  few 
particles  of  pyrites.  Towards  the  top  the  layers  become 
fine  grained  and  contain  thin  streaks  of  linonite  iron  ore. 

Following  are  ten  feet  of  red  shale  like  number  2. 

(6)  This  member  comprises  ten  feet  of  fine  grained  yellow 
sandstone. 

The  next  sixty  feet  are  concealed.  The  soil  is  sandy, 
yellow  in  color,  and  contains  considerable  vegetable  matter, 

(7)  Seventy-five  feet  of  hard  grayish  sandstone,  with  beds 
of  shale.     The  next  seventy  feet  are  concealed. 

(8)  Forty  feet  of  light  green  sandstone,  fine  grained. 

(9)  Fifteen  feet  of  grayish,  dark  green  and  black  sandy 
shales.     The  shales  show  a  strong  resemblance   to   those 
found  in  the  carboniferous  coal   measures  of  Pennsylvania. 
Ripple  marks  and  mud-flows  are  evidence  that  the    beds 
were  deposited  in  shallow  water. 

The  following  plant  fossils  were  found  here:  Macro- 
t&nioptcris  magnifolia,  Cheirolepis  munsteri,  Baiera  munste- 
riana,  Loperia  simple  x-=Bambusium  of  Fontaine. 

There  were  found  in  addition  to  these  a  few  fern  frag- 


II 

ments  doubtfully  referred  to  Mertensides  bullatus,  a  doubtful 
species  of  Equisetum  and  fossils  which  appear  to  be  roots 
of  some  sort.  The  Macrotceniopteris  is  very  abundant,  the 
others  not  so  common. 

It  is  evident  that  this  was  the  site  of  one  of  the  numerous 
marshes  similar  to  those  of  the  Triassic  coal  fields  of 
Virginia. 

In  the  general  remarks  on  these  rocks  further  discussion 
will  be  made  of  these  fossils. 

(10)  Above  these  beds  of  shale  come  thirty-five  feet  of  red 
sandstone  and  red  shale.  A  few  worn  fragments  of 
M.  magnifolia  and  an  Equisetum  were  the  only  fossils 
found.  With  the  inflowing  of  sand  and  the  changed  con- 
ditions, the  plants  seem  to  have  died  out.  Few,  if  any,  fos- 
sils were  to  be  seen  in  the  rocks  above.  At  the  top  of  these 
beds  are  fifteen  feet  of  soft  red  shales,  like  those  before  de- 
scribed. 

(i  i)  Twenty  feet  of  fine  grained  yellow  sandstone. 

(\2)  Ten  feet  of  red  shales,  soft  and  crumbling. 

(13)  Forty-five    feet    of    massive   beds    of  a  light  col- 
ored,  almost    white     sandstone,    it   is   fine    in    grain   and 
slightly   calcareous,  and   contains   a   good   deal   of    mus- 
covite. 

(14)  Fifteen  feet  of  shaly  rock,  some  of  which  is  soft  and 
red  like  that  before  described ;  some  is  harder  and  greenish 
in  color.      There   are   also   some   beds  of  a  greenish  gray 
sandy  rock.      It  is   very  fine  grained,  but  rather  soft  and 
earthy.    It  is  also  slightly  calcareous  and  contains  mica. 

The  next  seventy  feet  are  concealed. 

(15)  Fifteen  feet  of  red  shales. 

(16)  Eighty  feet  of  fine  grained,  compact  sandstone,  con- 
taining many  scales    of  mica.     It   is   light    yellowish    to 
greenish  in  color   and    resembles    somewhat   the   eleventh 
member  of  the  series. 

(17)  Ten  feet  of  red  shales. 


I* 

(18)  Thirty    feet  of  fine   to    coarse  grained   sandstone, 
yellowish  gray  in  color. 

(19)  Fifteen  feet  red  shales,  same  as  previous  shales. 

(20)  Fifty  feet  of   hard,  fine  grained    sandstone.     The 
beds  are  generally  light  green   in   color,  though  some  of 
them  are  light  yellow  to  gray.   The  sandstone  is  micaceous 
and   in   general    appearance   and    texture    resembles   the 
sandstone   members  just  previously  described,  though  for 
some  reason  it  has  suffered  a  change  in  color. 

(21)  Red  shales,  five  feet. 

(22)  Eighty  feet  of  irregular  beds  of  shale  and  gray  sand- 
stone. 

(23)  For  eighty  feet  the  exposure  is  not  particularly  good, 
owing  to  growth  of  vegetation.     The  layers  seen  in  place 
are  made  up  of  an  exceedingly  hard,  compict,  fine  grained 
sandstone    of    a   dark   bluish   black   col>r.     The  rock  is 
tough  and  when  struck  with  a  hammer  rings  distinctly.    It 
weathers  into  round,  smooth  boulders  which  at  first  sight 
strongly  resemble  some  form  of  trap,  or  at  least  a  baked 
rock  of  some  sort. 

There  are  irregular,  rounded,  flat  makings  looking  like 
obscure  forms  of  algae. 

(24)  One  hundred  and  thirty  feet  of  light-colored  grayish, 
almost  white,  sandstone,  lying  in  fine  grained,  compact  beds. 
Some  of  the  layers  are  strongly  micaceous. 

A  few  plant  remains  were  seen,  resembling  a  form  of 
Equisetuin. 

The  beds  for  the  next  two  hundred  feet  are  concealed. 
From  what  indications  could  be  seen  it  is  probable  that  a 
large  part  of  the  concealed  portion  is  made  up  of  beds  of 
sandstone  similar  to  those  just  described. 

(25)  The  remaining  seventy  feet  up  to  the  dike  comprise 
beds  of  vari-colored  slates  and  shales.     These  have  in  some 
cases  suffered  metamorphism  as  a  result  of  the  eruption  of 
the  trap.      Secondary  minerals,  however,  are   but  scantily 


13 

developed,  most  of  the  action  in  this  direction  being  confined 
to  alterations  in  color  and  the  formation  of  microlites. 

The  presence  of  many  cracks  and  joints  in  these  rocks  i 
make  it  difficult  to  measure  the  dip  accurately.     A  general 
average  of  several  measurements  is  19°  W.  N.  W.     As  this' 
comes  reasonably  close  to  many  of  the  dips  in  the  lower 
part  of  the  section,  it  is  probably  nearly  correct. 

The  following  description  will,  it  is  hoped,  give  an  idea 
of  the  general  character  of  these  beds.  ^It  was  intended  at 
first  to  make  a  detailed  study  of  thfse  rocks,  chemically 
and  microscopically,  but  lack  of  time  did  not  permit. 
Further  work  will  be  done  on  them  later. 

The  first  eighteen  to  twenty  feet  above  the  member  last 
described  are  made  up  of  black,  hard  and  brittle  beds,  with 
a  number  of  layers  of  gray  shale.  These  rocks  are 
cracked  and  broken  into  irregular  blocks. 

Following  come  six  feet  of  rock  in  general  like  the 
former,  but  having  many  streaks  of  a  serpentine  colored 
material.  These  greeni>h  layers  become  more  abundant  at 
the  upper  part,  and  pass  into  a  whitish  shaly  rock.  These 
beds  alternate  with  more  greenish  rock. 

Next  comes  a  rock  which  is  rather  persistent,  occurring 
in  several  different  beds.  It  is  hard,  blackish,  with  a  faint 
blue  tinge.  It  is  brittle  and  has  a  fracture  like  that  of  slate. 

On   the  surface  it  is  spotted  with  grayish   black   marks. 
A  microscopic  examination  revealed  the  presence  of  very , 
minute  dust-like  crystals  of  magnetite.     These  are  scattered 
pretty  uniformly  through  the  rock,  but  they  have  frequently 
crowded  together  to  produce  rounded  opaque  spots. 

This  gives  the  general  appearance  of  a  volcanic  glass  in 
which  swarms  of  microhtes  have  appeared,  though  of 
course  this  rock  has  not  the  glassy  character.  (For  illustra- 
tion see  plate,  Fig  2.) 

The  remaining  rocks  are  mostly  green,  black  and  pink 
shales  or  slates.  A  common  rock  is  a  light  ytllowish  green 


shale.  Microscopically  it  is  seen  to  consist  of  fine  grains 
lying  in  a  base,  which  in  ordinary  light  is  clear  and  color- 
less, but  which  polaiizes  to  a  gray  blue  with  a  few  patches 
of  yellow.  A  high  power  shows  the  presence  of  many  fine 
transparent  needles,  which  polarize  with  parallel  extinction. 
This  rock  has  layers  in  which  are  crowded  together  many 
small  crystals  of  apatite.  (See  plate,  Fig.  i.)  This  rock  occurs 
within  twenty-five  or  thirty  feet  of  the  lower  side  of  the  dike. 

GENERAL  REMARKS  ON  THE  RELATION  OF 
THE  ROCKS. 

It  will  be  noticed  from  the  description  given  of  the  rocks 
in  the  section  measured  that,  excluding  the  lower  part, 
which  is  concealed,  the  prevailing  character  of  the  rock  is 
a  fine  grained  sandstone.  Shale  is  not  very  abundant  aside 
from  the  thin  beds  of  the  soft  red  shale.  Of  course,  in 
regard  to  the  lower  .part  there  is  doubt  as  to  the  character 
of  a  large  part  of  it.  It  must  be  considered,  also,  in  the 
upper  part,  that  those  portions  of  the  column  which  are 
concealed  are  in  general  lower  in  elevation  than  the  parts 
which  are  well  shown.  This  would  indicate  soft  rocks,  such 
as  shales.  Still,  in  spite  of  this,  it  seems  safe  to  say  that 
the  greater  part  of  the  formation  is  composed  of  sandstone. 

Now,  in  the  region  of  Bucks  and  Montgomery  counties 
in  Pennsylvania,  the  researches  of  Lyman  have  shown  that 
the  greater  part  of  the  formation  is  shale,  excepting  the 
lowest  members — the  Norristown  division.  On  the  other 
hand,  in  Virginia  and  Maryland  coarse  conglomerates  and 
large  stones  or  groups  of  stones  occurring  in  the  finer  sand- 
stones are  remarkable  features  of  the  formation.1 

From  this  it  would  seem  that  the  formation  in  York 
county  occupies  an  intermediate  position  between  the  beds 
in  Bucks  county  and  those  in  Virginia.  For  if  the  material 
came  from  the  south,  the  larger  part,  such  as  boulders, 

1  Dana's  Manual,  1895,  p.  745. 


15 

would  be  left  near  the  source,  while  the  clays  and  muds 
would  be  carried  furthest.  That  the  formation  in  this  part 
of  York  county  is  of  the  same  age  as  that  further  south  is 
indicated  by  the  fossils  which  were  named  on  a  previous  page. 

B.  S.  Lyman  has  attempted  a  correlation  of  the  fossils 
of  the  Trias.1  He  places  all  the  important  plant  fossils,  such 
as  those  occurring  in  Virginia,  towards  the  bottom  of  the 
Gwynedd  shales,  the  second  division  in  the  New  Red  of 
Bucks  and  Montgomery  counties.  Thus  in  Hanover  and 
Cumberland  counties,  Virginia,  occur  Macrotceniopteris 
magnifolia,  Cheirolepis  munsteri,  Equisetum  rogersi,  etc., 
which  are  the  species  found  below  York  Haven. 

From  this  it  would  seem  that  the  formations  here  studied 
belong  in  the  lower  part  to  the  Norristown  shales  of  Ly- 
man's  division,  and  extend  in  part  into  the  Gwynedd.  Certain 
fossils  found  in  York  county,  at  Goldsboro  several  miles 
above  York  Haven,  are  referred  doubtfully  to  the  Lansdale 
beds  by  Lyman.2 

In  the  absence  of  cross  sections  connecting  the  lower  and 
upper  beds  in  York  county,  any  speculations  regarding 
their  relative  positions  are  of  questionable  value.  A  general 
section  might  be  constructed  across  the  county  from  the 
observations  already  published,  but  it  would  be  of  no  value. 

The  remainder  of  this  paper  is  given  up  to  a  description 
of  the  two  dikes  mentioned  in  the  introduction,  beginning 
with  the  one  at  Stony  Brook. 

THE  STONY  BROOK  DIKE. 

By  reference  to  the  map  the  position  and  length  of  this 
dike  may  be  seen.  It  is  about  twelve  miles  long,  beginning 
in  the  Cambrian  limestone  east  of  York,  and  running  south 
through  the  slates  and  schists  indicated  on  the  map. 

1  Proceedings  Am    Phil.  Soc.,  vol.  33,  pp.  204—215. 

2  See  Pa.  Geo.  S.  An.  Report,  1887;  also,  Summary  Final  Report,  vol.  3,  p.  2610. 


i6 

Its  course  maybe  traced  by  the  trap  rubbish  along  the  sur- 
face. It  has  been  referred  to  by  Persifor  Frazer  as  the 
Loganville  dike.1 

.  It  is  here  called  the  Stony  Brook  dike,  since  the  most 
important  exposure  of  it  is  in  the  cut  of  the  Frederick 
Division,  Pennsylvania  Railroad,  at  the  village  of  Stony 
Brook,  four  miles  east  of  York. 

It  was  hoped  that  at  the  village  of  Enterprise,  on  the 
Peach  Bottom  Railroad,  southeast  of  York,  where  there 
runs  a  branch  of  the  Codorus  Creek,  the  dike  would  be 
exposed  in  its  natural  position.  Such  is  not  the  case, 
however;  consequently,  no  evidence  of  metamorphic  action 
of  the  trap  was  found.  Numerous  trap  boulders  occur, 
mingled  with  fragments  of  quartzite  and  chlorite  schist. 

The  interesting  fact  was  noticed  here  that  some  of  the 
boulders  when  struck  possessed  great  resonance.  Of 
two  pieces  lying  side  by  side,  one  when  struck  rang 
almost  like  a  phonolite,  while  the  other  did  not  have  this 
property.  As  the  fragments  were  seemingly  alike  in  all 
other  respects,  the  difference  was  probably  due  to  some 
difference  in  their  position  in  the  ground. 

At  the  railroad  cut  at  Stony  Brook  the  dike  is  well  exposed 
and  its  width  easily  measured ;  it  is  seventy-four  feet  wide. 
Its  contact  with  the  limestone  is  sharp  and  distinct.  At 
this  point  the  dike  makes  a  small  elevation,  which  soon 
fades  away.  The  limestone  adjoining  the  dike  is  highly 
crystalline,  but  contains  no  secondary  crystallizations  of 
minerals.  It  is  whitish  in  color,  with  thin  blackish  streaks. 
There  are  also  some  thin  beds  of  shale. 

Perhaps  the  most  striking  feature  of  the  limestone  here 
is  a  layer  of  conglomerate,  differing  from  ordinary  rocks 
of  this  name  in  the  fact  that  the  material  is  all  limestone. 
It  has  probably  resulted  from  the  cementing  together  of 
limestone  pebbles  and  fossils,  which  have  since  been  altered 

1  Report  C,  Pa.  Geo.  Survey,  p.  95.  ,  ,v>    -..  : 


17 

by  metamorphic  action.  Persifor  Frazer  has  mentioned  the 
occurrence  of  a  similar  conglomerate  near  Columbia,  Penn- 
sylvania.1 This  limestone  conglomerate  appears  to  be  a 
somewhat  common  occurrence  in  the  older  limestones  ,  of 
Pennsylvania.  C.  D.  Walcott  has  called  such  formations 
"  Intraformational  Conglomerates,"2  and  in  his  report  on 
York  county,  before  mentioned,  he  figures  such  an  occurr- 
ence near  York. 

Prof.  J  Peter  Lesley,  in  speaking  of  this  dike,  and  one 
west  of  York,  says  :8  "  In  this  case,  as  in  that  of  the  Gon- 
shohocken,  Montgomery  county,  Pa.,  dike,  no  production 
of  white  marble  appears  as  due  to  igneous  action."  This  is 
beyond  all  doubt  true,  as  at  many  localities  in  this  same  lime- 
stone belt,  at  wide  distances  apart,  fine  grained  white  marble 
appears  where  there  is  no  evidence  at  all  of  igneous  action. 
In  fact,  in  York  county  the  limestone  shows  great  varia- 
tion, ranging  fiom  a  hard,  compact  limestone  to  a  fine  white 
marble.  In  some  places  all  gradations  from  one  form  to 
the  other  may  be  observed. 

The  metamorphism  is  regional  and  not  local,  and  proba- 
bly occurred  long  before  the  trap  was  erupted. 

It  may,  however,  seem  strange  that  the  limestone  at  the 
junction  of  the  dike  shows  no  evidence  of  igneous  action. 
Toe  composition  of  the  limestone,  as  shown  in  the  following 
analysis,  should  be  sufficient  to  explain  this  : 

ANALYSIS  OF  LIMESTONE  FROM  STONY  BROOK. 
C*CO3     ...........    .    .    96.61 

MgCO3   .............       1.40 

StO2    ..............      i.oo 


Carbon 


1  Pa.  Geo.  Survey,  ReportC,  p  132. 

*  Bull.  Gco.  S    Amer.,  vol.  5,  pp.  192-98. 

8  Summary  Final  Report,  Pa.  G.  S.,  1892.  p.  454. 


18 

It  will  be  observed  that  the  percentage  of  MgO,  SiO2,  etc. 
is  small — not  enough,  in  fact,  to  allow  the  formation  of 
secondary  minerals  in  the  limestone.  The  minerals  usually 
found  in  such  instances  are  those  like  the  amphiboles,  garnets, 
andalusite,  pyroxenes,  or,  in  short,  those  requiring  a  high 
percentage  of  Mg,  Al,  Fe,  as  well  as  silica.  The  fact  that 
the  limestone  in  the  present  instance  is  over  96  5  per  cent 
pure  calcium  carbonate  would  seem  to  be  sufficient  reason 
for  the  absence  of  secondary  minerals.  This  being  so,  it 
might  naturally  be  expected  that  the  only  effect  of  the 
igneous  eruption  would  be  the  dissolving  of  part  of  the 
limestone  by  the  trap.  Such,  indeed,  seems  to  be  the  case, 
for  on  each  side  of  the  dike  occur  six  to  eight  inches  of  a 
greenish  rock,  lighter  in  color  and  finer  grained  than  the 
trap.  A  partial  analysis  of  this  rock  showed  the  presence 
of  16  per  cent  of  lime,  carbon  dioxide  being  absent.  The 
trap  proper  contains  9  per  cent,  as  the  following  analysis 
shows.  A  mean  of  several  analyses  gave  the  following 
.result : 

TRAP  FROM  STONY  BROOK. 

SiO2     .    ,    ...    .-  .    .    .    .    .  :«;    .    .  46.78 

TiO2    .    .    .       :,   .    .   .    .  u    .    J  ..    .  0.99 

CaO     .    .    .    .    .......    .    .    .  9.1 1 

MgO   .    .    .    .    ,    .    .    .    .    .       ,  i,    .  7.38 

Na2O   .    .    .    . --.-.•  ...>    .    ...    .    .. -.-   .  5.10 

K20     ........    ,,/   .  ...   ,    .  052 

Li2O    .    . trace 

A1203 .    ,    .    .  19-28 

Ft-2O3 ,  6.1 1 

FeO 4.16 

CoO trace 

MnO trace 

H2O.no° ,  0.05 

HO  --  110° 0.06 


19 

BaO none. 

SrO     .    .    % " 

CO2 

P2O6 .  not  test. 

S  .  trace. 


99-54 

In  regard  to  the  presence  of  the  oxide  of  cobalt  a  word 
of  explanation  is  perhaps  needed. 

In  almost  all  the  analyses  when  the  magnesium  ammo- 
nium phosphate  precipitate  was  dissolved  off  the  filter  and 
evaporated  in  nitric  acid,  a  rose  red  color  was  noticed 
towards  the  end  of  the  evaporation.  Some  of  this,  very 
likely,  was  due  to  manganese,  but  the  bead  test  seemed  to 
indicate  the  presence  of  very  minute  quantities  of  cobalt. 
It  was  hoped  that  by  taking  large  amounts  of  the  rock 
more  certain  evidence  of  the  presence  of  this  element  would 
be  found.  Such  was  not  the  case,  however.  Proof  of  the 
presence  of  cobalt  or  nickel  in  appreciable  amount  in  these 
rocks  would  be  of  considerable  interest.  At  present  it  is  a 
subject  for  further  investigation.  The  sulphur  present  is 
probably  all  there  as  pyrites,  since  a  few  specks  of  that 
mineral  were  observed  in  the  rocks. 

The  ferrous  iron  was  determined  by  decomposition  with 
sulpnuric  acid  in  sealed  tubes. 

The  description  of  the  trap  is  here  appended. 

MICROSCOPIC  CHARACTER   OF  THE  TRAP. 

The  trap  at  Enterprise,  near  the  lower  end  of  the  dike,  has 
the  ophitic  structure  of  diabase.  (See  plate,  Fig.  5.)  The 
base  is  entirely  granular  and  shows  many  places  clouded 
with  inclusions.  The  feldspar,  which  appears  to  be  labra- 
dorite,  extinction  angle=i8°3o'  to  I9°3(/,  has  altered  in 
•part,  forming  the  usual  decomposition  products.  Pale 


20 

brown  angite  occurs  mostly  in  grains;  also  in  long  columns. 
No  crystal  outlines  were  noticed.  The  pyroxene  has  begun 
to  pass  to  a  diallage  structure,  though  not  to  the  extent 
that  is  shown  in  the  rock  at  Stony  Brook.  Considerable 
magnetite  is  present,  and  hornblende  occurs,  apparently  as 
an  alteration. 

At  the  exposure  at  Stony  Brook  the  rock  is  in  general 
the  same.  It  is  finer  grained  and  has  suffered  more 
decomposition.  There  is  much  decomposed  feldspar  and 
the  field  is  cloudy.  1  he  base  is  granular.  The  feldspar  is 
apparently  labradorite,  while  the  pyroxene  has  much  diallage 
structure.  Hornblende  is  rather  common  and  in  some  places 
are  veins  of  secondary  hornblende  intergrown  with  microlitic 
feldspar  and  magnetite.  (See  plate,  Fig.  6.)  Towards  the 
outer  edges  of  the  dike  the  pyroxene  is  almost  all  ortho- 
phombic.  When  thin  sections  are  examined  in  reflected 
light  the  crystals  show  the  schiller  effect  of  bastite.  Run- 
ning up  and  down  through  the  trap  are  several  veins  of  de- 
composed material  consisting  of  hornblende  and  completely 
saussuritized  feldspar. 

THE  DIKE  AT  YORK  HAVEN. 

This  dike,  which  is  notable  on  account  of  its  size  and 
extent,  is  located  just  above  the  station  of  York  Haven,  on 
the  Northern  Central  Railroad,  on  the  Susquehanna  River. 

It  is  well  displayed  by  the  cut  of  the  railroad  and  in  a 
quarry  formerly  operated  here. 

It  extends  across  the  river  into  Lancaster  county  and  is 
exposed  in  the  same  manner  there  as  on  the  York  county 
side. 

la  the  river  are  numerous  boulders  of  the  rock,  which  in 
times  of  low  water  almost  fill  up  the  channel. 

The  width  of  the  trap  cannot  be  ascertained  with  any 
degree  of  certainty,  since  the  contact  of  the  dike  and 'the 


21 

adjacent  rock  is  concealed  on  each  side.  It  is  exposed 
for  over  two  hundred  feet  in  its  natural  position,  beginning 
at  the  lower  part.  Along  the  river  it  makes  an  elevation, 
of  a  hundred  feet  or  more ;  back  in  the  country  this  is  lost 
in  a  general  range  of  hills,  and  its  presence  is  known  only 
by  means  of  surface  t>oulders.  The  trap  occurs  in  compact 
masses,  is  rather  easily  worked  for  building  purposes,  and 
formerly  commanded  a  ready  sale  in  York,  Baltimore  and 
other  cities. 

In  regard  to  the  intrusive  or  extrusive  nature  of  the  trap 
the  evidence  is  not  very  satisfactory.  On  the  upper  side 
the  first  sedimentary  rock  seen  is  evidently  not  in  contact 
with  the  trap  and  has  not  suffered  any  metamorphism  due 
to  the  presence  of  an  igneous  eruption.  On  the  lower 
side  the  contact  is  not  sharply  exposed.  As  nearly  as  can 
be  seen,  however,  the  trap  does  not  lie  conformably  on  the 
sedimentary  rocks  below,  but  appears  to  break  across  the 
beds.  These  lower  beds  have  suffered  undoubted  meta- 
morphism. 

The  texture  of  the  rock  is  rather  dense  wherever  ex- 
posed. In  passing  from  the  lower  part  to  the  upper,  an 
increase  in  the  size  of  the  grains  is  noticed,  accompanied  by 
a  change  in  the  character  of  the  rock.  This  will  be  brought 
out  more  fully  in  the  remarks  under  the  microscopic 
character  of  the  trap. 

Towards  the  middle  of  the  dike  a  columnar  structure  like 
that  in  basalt  is  noticeable.  At  the  lower  edge  the  trap 
has  broken  into  thin  layers,  presenting  the  appearance  of 
upturned  beds  of  sedimentary  rock. 

The  above  observations  tend  to  an  intrusive  rather  than 
an  extrusive  origin. 

MICROSCOPIC    CHARACTERS. 

It  was  stated  that  the  trap  at  the  lower  side  is  fine  in 
grain.  The  rock  consists  of  plagioclasc  feldspar,  augite, 


22 

dark  brown  mica,  hornblende  and  titaniferous  iron.  The 
feldspar  is  labradorite.  Colorless  augite  occurs  in 
both  grains  and  the  irregular  columnar  patches  like  those 
in  diabase  rocks.  The  greater  part  of  the  augite,  however, 
is  in  well  formed  crystals  showing  the  usual  cross 
cleavage. 

This  gives  to  the  rock  a  pronounced  basaltic  appearance. 
(See  plate,  Fig.  3.) 

Dark  brown  mica  is  rather  common  in  scales ;  no  crystal 
faces  are  shown.  In  some  places  along  the  edges  and 
between  the  crystals  of  augite  occur  patches  of  hornblende. 

The  base  is  fine  granular  and  in  m  my  places  is  clouded 
with  inclusions  and  microlites,  replacing  almost  entirely 
the  pyroxene.  Very  small,  colorless  needles,  visible  with 
the  higher  powers,  occur  in  places.  They  are  possibly 
apatite. 

This  rock  is  evidently  a  dolerite. 

The  greater  part  of  the  trap  here,  however,  consists  of 
the  coarse  grained  type  with  a  gabbro  structure.  (See  plate, 

Fig.  4-) 

The  feldspar  has  a  high  angle  of  extinction,  varying  from 
24°  to  32°.  This  is  rather  high  for  labradorite.  It  may, 
perhaps,  belong  to  one  of  the  mixtures  between  labradorite 
and  anorthite.  The  high  percentage  of  CaO  and  rather 
low  percentage  of  Na2O  (see  analysis)  indicates  an  approach 
to  the  anorthite  molecule. 

The  pyroxene  has  passed  almost  entirely  to  the  diallage 
structure.  No  augite  crystals  were  noticed.  Mica  and 
hornblende  are  present,  and  inclosures  of  titanic  iron 
common. 

The  feldspar  has  begun  in  some  places  to  show  the  hazy 
appearance  due  to  decomposition  and  formation  of  saus- 
surite. 

The  following  is  an  average  analysis  of  the  trap  from 
near  the  middle  of  the  dike  : 


23 

ANALYSIS  OF  TRAP  FROM  YORK  HAVEN. 

SiO2 45.82 

TiO2 6.07 

A1203      1770 

Fe2O3 2.11 

FeO 6.15 

MnO trace. 

CoO trace. 

CaO 13.00 

MgO 6.66 

BaO    | 

SrO    .} none- 

K2O 0.82 

Na2O 2.42 

Li2O trace. 

Cr9O,  ) 


,* 

J 


not  tested  for. 


100.75 

On  the  presence  of  cobalt  oxide,  see  the  remarks  under 
the  analysis  of  the  Stony  Brook  dike. 

A  feature  of  the  trap  is  the  large  number  of  veins  of 
augitic  material  which  run  for  long  distances  in  all 
directions  through  the  rock.  Sometimes  long  needles  of 
zeolites  are  intergrown  with  the  altered  veins. 

In  the  more  altered  parts  of  the  trap  occur  veins  of 
secondary  minerals,  forming  whitish  masses,  in  which  are 
long,  needle-like  zeolites,  quartz  and  small,  perfectly  formed 
sphenes.  Lustrous  plates  of  bronzy  pyroxene  are  not 
uncommon. 

Biotite  occurs  in  plates  a  quarter  inch  in  size. 

On  the  exposed  surfaces  of  the  rock  occur  immense 
numbers  of  small  chabazite  crystals,  and  also  considerable 
stilbite.  Analyses  of  these  minerals  have  been  published.1 

i  C.  H.  Ehrenfeld,  Jour.  An.  and  App.  Chem.,  vol.  6  (2) ;    vol.  VII  (i). 


24 

GENERAL  SUMMARY  OF  RESULTS.' 

Of  the  section  measured  in  the  Trias  up  to  York  Haven, 
the  lower  part  probably  represents  the  Norristown  of 
Lyman. 

In  the  upper  part  the  presence  of  plant  fossils  character- 
istic of  the  coal  fields  of  Virginia  marks  a  connection 
between  these  beds  and  those  of  the  South. 

This  part  of  the  formation  probably  corresponds  to  the 
lower  portion  of  the  Gwynedd  of  Lyman. 

The  traps  consist  of  dolerite,  gabbro  and  diabase. 

At  York  Haven  the  original  magma  was  basaltic. 

The  lower  part  of  the  dike  still  has  a  basaltic  structure, 
while  the  middle  and  upper  portions  have  become  coarse 
grained  with  a  gabbro  structure. 

The  Stony  Brook  dike  is  a  diabase.  It  has  suffered 
considerable  change  and  has  developed  a  large  amount  of 
orthorhombic  pyroxene. 


ACKNOWLEDGMENT. 

This  work  was  carried  out  under  the  direction  of  Pro- 
fessor Amos  P.  Brown,  and  I  would  express  to  him  my 
most  sincere  thanks  for  the  interest  he  has  taken  in  the 
work  and  for  the  valuable  instruction  received  from  him. 

To  Professor  Edgar  F.  Smith  I  wish  to  extend  my 
grateful  thanks,  not  only  for  the  instruction  received  from 
him,  but  for  his  kindness  to  me  as  a  friend. 


ADDENDA. 

At  bottom  of  plate,  line  six,  read  vein  for  view. 

The  figures  all   show  magnification  of   35  diameters, 
and  except  Fig.  2,  were  taken  between  x  nicols. 


1.  Metamorphosed  shale  with  apatite,  York  Haven. 

2.  Slate  showing  aggregates  of  magnetite,  York  Haven. 

3.  Dolerite  from  York  Haven. 

4.  Gabbro  from  York  Haven. 

5.  Diabase  from  Enterprise. 

6.  View  of  Hornblende  in  diabase,  Stony  Brook. 


RETURN     EARTH  SCIENCES  LIBRARY 
TO—  ^                                                  642-2997 

LOAN  PERIOD  1 
1  MONTH 

2 

3 

4 

5 

6 

ALL  BOOKS  MAY  BE  RECALLED  AFTER  7  DAYS 

Books  needed  for  class  reserve  are  subject  to  immediate  recall 

DUE  AS  STAMPED  BELOW 


FORM  NO.  DD8 


UNIVERSITY  OF  CALIFORNIA,  BERKELEY 
BERKELEY,  CA  94720 


7  & ' 


e 


» 


